1. Field of the Invention
The present invention relates to a loudspeaker, and more particularly a loudspeaker cabinet.
2. Related Art
There have been a variety of proposals for suppressing undesired resonance in the loudspeaker cabinet, thereby allowing the sound to travel at an increased speed and rise at the beginning of sound reproduction. The loudspeaker cabinet is made of thick plates in the hope of suppressing undesired resonance in its closed space, but such loudspeaker cabinet is not satisfactory. The loudspeaker cabinet of ceramic is found satisfactory to some extent, but the shaping of the cabinet is difficult because of its hardness, and its heaviness is a problem, also. Still disadvantageously, it produces accompanying sound inherent to the material.
The inventor realized that undesired vibration is caused by deformation or distortion in the cabinet and that the cabinet if pre-deformed or pre-stressed is capable of preventing occurrence of significant resonance in its closed space. The inventor has proposed speaker cabinet of duralumin that is pre-stressed by using screw rods (see Japanese Patent 2000-224682(A)). The metal cannot be welded, and lacks ductility to and can thus be easily broken by bending. Such difficulty in workability makes it difficult to provide a cabinet structure that can be pre-stressed still more.
One object of the present invention is to provide a loudspeaker cabinet structure which can be so pre-stressed as to suppress undesired resonance effectively.
The inventor discovered that the stressing in the form of compression is most effective to suppress undesired resonance in the loudspeaker cabinet.
To attain this object a loudspeaker comprising a cabinet and a loudspeaker unit fixed to the inside of said cabinet is improved according to the present invention in that said cabinet comprises a hollow conical assembly comprising two conical bodies of high-rigidity metal, one press-fitted into the other; said hollow conical assembly having front and rear plates closing its front and rear openings.
The press-fitting of one of the high-rigidity conical bodies into the other by applying an increased pressure causes an extraordinary stress to occur in the hollow conical assembly far beyond the stress caused by pulling force. The conical body needs to be made of a sheet of metal of high-rigidity such as steel or duralumin of sufficient thickness.
The front and rear plates may be press-fitted in the front and rear openings of the hollow conical assembly, and these plates are circular disks whose circumferences converge inward, the larger diameters of the circular disks being somewhat larger than the diameters of the front and rear openings of the hollow conical assembly.
Use of circular disks whose circumferences converge inward assures that the circular disks be firmly pushed into the opposite openings of the hollow conical assembly, permitting application of strong pressure to the circular disks to cause compression stress in the hollow conical assembly.
The loudspeaker unit may be fixed to the front plate by tightening screw rods, thereby applying an increased compression stress to the loudspeaker unit.
Application of compression stress to the loudspeaker unit will effectively suppress undesired vibration of the loudspeaker unit of metal.
The front and rear plates may be pulled toward each other by tightening screw rods, thereby fixing the front and rear plates to the hollow conical assembly.
The tightening of the screw rods will keep the front and rear plates tightly fitted into the front and rear openings of the hollow conical assembly without allowing the looseness to appear in the front and rear closed ends of the hollow conical assembly.
The front and rear plates may be annular plates each having an inward converging aperture made at its center, and a disk fitted in the inward converging aperture; and the disks fitted in the front and rear plates may be pulled toward each other by tightening screw rods, thereby fixing the front and rear plates to the hollow conical assembly.
This arrangement will allow application of increased compression stress to the front and rear plates.
In assembling, a press machine is used in applying an extraordinary pressing force to one conical body to push it into the other conical body, thus providing a hollow conical assembly; and the front plate having the loudspeaker unit fixed thereto is press-fitted into the front opening of the hollow conical assembly with the aid of the press machine; and then the rear plate is press-fitted into the rear opening of the hollow conical assembly with the aid of the press machine, also.